Application of metal organic frameworks (MOFs) to capturing CO2 directly from air

Increased CO2 concentration in the atmosphere is increasingly linked to climate change. With the aim of developing next-generation carbon capture technologies; this thesis focuses on the use of solid amine-functionalized metal-organic frameworks (MOFs) for CO2 capture from air. MOFs are promising because of their tunability and high porosity. However, many considerations are required for their practical utilization. 1. High equilibrium adsorption capacity at ultra-dilute CO2 concentrations, 2. Incorporation of MOFs into practical substrates that can provide low pressure drops at high flowrates of air, and 3. Process analysis that takes into account various thermodynamic and kinetic factors. This thesis studied MIL-101(Cr) and Mg2(dobpdc) frameworks functionalized with various amines for CO2 adsorption at direct air capture conditions. Additionally, diamine-appended Mg2(dobpdc) was immobilized on a practical honeycomb monolith substrate with an oriented MOF growth. This diamine-appended framework was further studied for CO2 adsorption in a packed bed experiment where different regimes of breakthrough profiles were identified using an equilibrium wave theory and the kinetics of CO2 adsorption was characterized using semi-empirical models. Overall, this thesis aims to further the understanding of the scientific community in various aspects that are critical for the use of novel adsorbents in a practical process.Ph.D

CO₂ Capture From Air

Presented during the Three Minute Thesis (3MT™) Competition on November 15, 2016 in the LeCraw Auditorium, Scheller College of Business at Georgia Tech.Lalit A. Darunte, Chemical and Bimolecular EngineeringRuntime: 03:12 minute

Exploring steam stability of mesoporous alumina species for improved carbon dioxide sorbent design

Many different metrics exist to assess the efficacy of a carbon capture sorbent, though one of the pivotal characteristics is stability on regeneration, most notably steam stability, which applies to steam stripping regeneration, a technique proposed for capture of CO 2 from humid flue gas. In this study, the steam stability of two different mesoporous alumina species is compared, with an aim to tune the synthesis methodology and the local structure and crystallinity of the samples to create a stable regenerable sorbent. The roles of calcination temperature and aminopolymer impregnation on sorbent stability and structure are also investigated using a wide range of characterization techniques to specifically probe the influence of the alumina support. We show through this study that support choice, and support stability, can play an important role in sorbent design for carbon capture. We highlight that regular crystallinity (such as in γ-alumina) hinders the formation of pseudo-boehmite, allowing a material to retain its CO 2 uptake. Further, we show that the addition of aminopolymers (PEI) can facilitate phase changes, however aminopolymers help maintain the mesoporosity of the sample, a key metric for CO 2 uptake. </p

Direct Air Capture of CO₂ Using Amine Functionalized MIL-101(Cr)

Direct adsorption of CO₂ from ambient air, also known as direct air capture (DAC), is gaining attention as a complementary approach to processes that capture CO₂ from more concentrated sources such as flue gas. Oxide-supported amine materials are effective materials for CO₂ capture from dilute gases, but less work has been done on metal organic framework (MOF) supported amine materials. Use of MOFs as supports for amines could be a versatile approach to the creation of effective amine adsorbents because of the tunability of MOF structures. In the present work, MIL-101­(Cr) materials functionalized with amine species are evaluated for CO₂ capture from simulated air. Two amines are loaded into the MOF pores, tris (2-amino ethyl) (TREN) and low molecular weight, branched poly­(ethylene imine) (PEI-800), at different amine loadings. The MIL-101­(Cr)-TREN composites showed high CO₂ capacities for high loadings of TREN, but a significant loss of amines is observed over multicycle temperature swing adsorption experiments. In contrast, MIL-101­(Cr)-PEI-800 shows better cyclic stability. The amine efficiency (mol CO₂/mol amine) as a function of amine loading is used as a metric to characterize the adsorbents. The amine efficiency in MIL-101­(Cr)-PEI-800 showed a strong dependence on the amine loading, with a step change to high amine efficiencies occurring at ∼0.8 mmol PEI/g MOF. The kinetics of CO₂ capture, which have important implications for the working capacity of the adsorbent, are also examined, demonstrating that a MIL-101­(Cr)-PEI-800 sample with a 1–1.1 mmol PEI/g MOF loading has an excellent balance of CO₂ capacity and CO₂ adsorption kinetics

Carbon Hollow Fiber-Supported Metal-Organic Framework Composites for Gas Adsorption

Supporting metal-organic frameworks (MOFs) on scalable contactors such as hollow fibers provides a practical way to expedite their use in large-scale industrial applications. Here, the development of carbon-hollow-fiber-supported MOFs as adsorbent composites for gas separation processes is reported. Moreover, this work provides an effective approach for the growth of MOFs on the surface of carbon hollow fibers that are successfully produced by pyrolysis of cross-linked Torlon hollow fibers. To fabricate MOF/carbon composites, the carbon hollow fibers are functionalized in different media to increase the surface hydroxyl groups prior to MOF growth. The MOF incorporation is performed by growing MOF-74 and UTSA-16 in the pores and on the outer surface of hollow fibers using dip-coating and layer-by-layer techniques. The MOF/carbon composites with relatively high MOF loadings (37-38 %) and porous structures are successfully fabricated, yielding film thicknesses as high as 10-15 μm. The MOF-74/carbon and UTSA-16/carbon composites exhibit surface areas of 266 and 211 m2 g-1, and pore volumes of 0.28 and 0.20 cm3 g-1, respectively. As a proof-of-concept, the CO₂ adsorption performances are evaluated and the MOF/carbon composites are shown to have relatively good CO₂ adsorption capacities of 2.0 and 1.2 mmol g-1 for UTSA-16 and MOF-74, respectively, at room temperature and 1 bar

Monolith-Supported Amine-Functionalized Mg₂(dobpdc) Adsorbents for CO₂ Capture

The potential of using an amine-functionalized metal organic framework (MOF), mmen-M₂(dobpdc) (M = Mg and Mn), supported on a structured monolith contactor for CO₂ capture from simulated flue gas is explored. The stability of the unsupported MOF powders under humid conditions is explored using nitrogen physisorption and X-ray diffraction analysis before and after exposure to humidity. Based on its superior stability to humidity, mmen-Mg₂(dobpdc) is selected for further growth on a honeycomb cordierite monolith that is wash-coated with α-alumina. A simple approach for the synthesis of an Mg₂(dobpdc) MOF film using MgO nanoparticles as the metal precursor is used. Rapid drying of MgO on the monolith surface followed by a hydrothermal treatment is demonstrated to allow for the synthesis of a MOF film with good crystallite density and favorable orientation of the MOF crystals. The CO₂ adsorption behavior of the monolith-supported mmen-Mg₂(dobpdc) material is assessed using 10% CO₂ in helium and 100% CO₂, demonstrating a CO₂ uptake of 2.37 and 2.88 mmol/g, respectively. Excellent cyclic adsorption/desorption performance over multiple cycles is also observed. This is one of the first examples of the deployment of an advanced MOF adsorbent in a scalable, low-pressure drop gas–solid contactor. Such demonstrations are critical to the practical application of MOF materials in adsorptive gas separations, as structured contactors have many practical advantages over packed or fluidized beds